I've been reading the LA Times articles on measuring teachers, and I wrote about it briefly. I've also written about another way to measure quality in teachers.
The problem is the thing you're measuring. If short-sighted superintendents or boards of education base salaries or advancement on test scores -- or, put another way, if teachers know that how much money they make depends on teaching kids to do well on a test -- more teachers than we would like will teach nothing that will not be on the test, and a few will cheat.
So how should you evaluate progress in kids? And progress at what? As I said in the post linked above, this system is limited to regular cognitive progress, thinking and learning stuff. Art, music, athletics, leadership, socialization, writing poetry or fiction-- None of these is captured in the test the State of California uses to measure elementary school kids. Measuring any of them is possible, but probably not in a system that can be reduced to numbers. "Your brush strokes are 10% better than last year, but your imagery is 5% more derivative."
Another problem is that the value added system, as I wrote before, "assumes that the student’s life is steady, that the only difference between this year and the last three is the teacher. If a kid’s score was down last year because his brother was shot, then another brother will be shot this year, and the next. If his dad wasn’t in jail two years ago, he won’t be this year. Sometimes that’s true."
I guess the answer here is that if you look at scores of kids for every teacher, every teacher will average the same number of kids with brothers who got shot.
Prediction: In sum, we have a good tool to measure one aspect of kids' progress. It is cheap and easy to use and to understand. Every other part of measuring progress is difficult and would be very expensive. Therefore, school districts will inevitably slide toward using it as the sole measure, to the detriment of kids and teachers.
Some school districts will use the opportunity for bad teachers to learn from good ones. Others will use it as a way to prune the payroll when they have to make budget cuts.
And I think our only hope is to have the test reflect at least all the cognitive things we want kids to learn.